Around three-and-a-half years after ending anti-retroviral therapy, the patient has no sign of infection.

German scientists led by Dr Kristina Allers, from Charite-University Medicine Berlin, wrote in the journal Blood online: "From these results, it is reasonable to conclude that cure of HIV infection has been achieved in this patient."

The donor stem cells replaced the patient's HIV-infected population of CD4 white blood cells. The stem cells had a genetic variant known to prevent invasions by the HIV virus.

After the transplant, it was found that HIV replication in the patient had stopped. However, doctors expected the virus to return as the patient's cancer-damaged immune system was being rebuilt.

The new follow-up study shows this did not happen. Instead scientists found successful reconstitution of "healthy" CD4 cells throughout the patient's body.

CD4 cells are vital "helper" T-cells which activate and direct other elements of the immune system.

The researchers wrote: "By monitoring the most common prognostic markers, HIV cannot be assessed in this patient."

British experts said they were impressed by the results, but argued that bone marrow transplants were not a practical way to treat HIV infection.